Internet Protocol (IP) version 4 (IPv4) is the fourth version of the IP, and IPv4 is one of the core protocols of standards-based internetworking methods on the Internet. IPv4 is a connectionless protocol for use in packet-switched networks that operates on a best effort delivery mode. The best effort delivery model does not guarantee delivery or assure proper sequencing or avoidance of duplicate delivery. These aspects, including data integrity, are addressed by an upper layer transport protocol, such as the Transmission Control Protocol (TCP) or User Datagram Protocol (UDP). IPv4 is still used to route most of the Internet traffic today, despite the ongoing deployment of a successor protocol, IP version 6 (IPv6).